The present invention relates to an engine brake controlling apparatus for controlling an engine brake by operating a lock-up clutch of an electronically controlled automatic transmission mounted on a vehicle.
Conventionally, a known technique is arranged such that a vehicle having a torque converter is provided with a lock-up clutch for effecting engagement and disengagement between input and output shafts of the torque converter in correspondence with a running state so as to realize low fuel consumption for the vehicle. This type of technique is disclosed in, for instance, Japanese Patent Laid-Open No. 35858/1981.
In a vehicle equipped with an automatic transmission, a speed-change stage is automatically determined in correspondence with a running state. If the driver returns an acceleration pedal in an attempt to reduce the vehicle speed, an engine brake is applied when the vehicle speed is greater than the engine speed. At this time, unless the lock-up clutch is engaged, the torque converter slips, so that the engine brake works less effectively than in a case where the lock-up clutch is engaged.
Accordingly, it is conceivable to provide an arrangement in which, in order to improve the efficiency of the engine brake, the lock-up clutch is made to engage when the number of revolutions of an output shaft of the torque converter has exceeded the number of revolutions of an input shaft thereof, thereby improving the working of the engine brake.
In this case, however, there is the possibility that, if a brake pedal is pressed suddenly, the engine stalls simultaneously with the locking of the wheels.